The subject matter disclosed herein relates to an operation method of an X-ray CT apparatus and an X-ray CT (Computed Tomography) apparatus, in particular to a method for detecting whether an X-ray CT apparatus can meet the requirement for scanning an object to be scanned and the CT apparatus and system using said detection method.
X-ray is known to be harmful to the tissues and organs of human body, so the manufacturers of X-ray CT apparatuses try their best to make the X-ray CT apparatuses they manufactured obtain better scan images with the lowest X-ray radiation amount as it can be. Thus an intelligent tube current control model has been invented and applied to X-ray CT apparatuses, which can ensure a uniform noise value among the scan images of all the cross sections obtained by using tube current of different magnitudes to each of the scanned cross sections. Currently, the tube current control model has been widely used in the field of CT apparatus and has become a very important characteristic of the CT apparatus and system.
For an existing CT apparatus having a tube current control model, the flow of executing a scan is as shown in FIG. 1, wherein a scout scan is performed on a patient in step 110 to obtain the scout scan data; in step 111 a doctor chooses the length of an area to be scanned according to the scout scan data; step 112 is that the doctor manually input the range of tube current value and the desired noise index after determining the range of the length of the area to be scanned; then in step 113, the CT apparatus performs the subsequent scanning according to the tube current and the noise index set by the doctor. Correspondingly, the operation interface of the CT apparatus having a tube current control model is as shown in FIGS. 2 and 3, and the operation mode thereof is as the following: the patient is sent into CT to be scanned, a scout scan is performed on the patient, and a scout scan image is obtained, as shown in FIG. 4. Then the tube current button on the user operation interface as shown in FIG. 2 is pressed to activate the tube current control box as shown in FIG. 3 to pop up a user operation interface for tube current control; proper noise index and range of tube current value are entered in the tube current control in FIG. 3 according to the data of the scout scan image, the button of “Confirm” in FIG. 3 and then the button of “Confirm” in FIG. 2 are pressed to perform the subsequent scanning.
However, the existing CT apparatus having a tube current control model have the following disadvantages:
First, if the doctor is not clear about the setting of the noise index of the operated CT apparatus, then when the doctor sets a noise index to scan the patient, the noise index of the resulted scan image is quite different from the value set by the user. This makes the doctor doubt the result of examination and even re-scan the patient, thus making the patient suffer from more X-ray radiation.
Second, when testing the function of the apparatus, failure of test sometimes occurs. After resetting the range of tube current and noise index in the corresponding positions as shown in FIG. 3, the previously failed testing item may pass smoothly. But sometimes, even if the range of tube current value and/or index are reset, the test still fails, thus the tester may become confused and wonder what on earth the appropriate range of test value should be.
Third, the noise index and the range of tube current value are independent from each other in the tube current control parameter input user operation interface of the existing CT system, as shown in FIG. 5. Therefore, in this tube current control interface, the input of the range of tube current value does not influence the input of the noise index, and vice versa.
Take the parameters as shown in FIG. 5 as an example, if the noise index is set to be 1.0, and the maximum tube current value is set to be 15 mA at the same time, then the whole scan can be carried out smoothly, as shown in FIG. 6. A phantom of a scanned object is extracted under such set parameters, and in the output image, it can be seen that the maximum tube current value is lower than 15 mA; obviously, a image with a noise index of 1.0 cannot be obtained. However, in the output image, we do see the characteristic of the noise index being 1.0. Such serious mismatch makes the scan image in a mess and with a lot of noise, as a result, it might be necessary to re-scan the patient, thereby making the patient suffer from more X-ray radiation.
Likewise, if the preset minimum value in the range of tube current value is comparatively large, for example, 200 mA, and for some patients, the doctor sets and inputs a noise index of 15, but in fact, it is possible that some tomographic images of the patient can reach the noise index of 15 only with a current of 150 mA, while unfortunately, the minimum value that is available in the system is 200 mA. Therefore, in the output scan image, the actual minimum tube current value is 200 mA, while the noise index is still shown to be 15. The noise index of such output image is not consistent with the actual noise index, which also makes the patient suffer from unnecessary radiation dosage.
In summary, in the existing X-ray CT apparatus having a tube current control model, since its two parameters, namely, the tube current value and the noise index are independent from each other, the setting and input of one parameter will not cause the input of the other parameter. Thus during operation, when the user inputs one parameter, the system cannot automatically display the range of the other parameter matching said input parameter. And the user has to set the other parameter according to his experience, and this may result in a great difference between the output scan image and the set parameters. Accordingly, the condition of the patient cannot be truly reflected or the patient is made to accept too much radiation. In addition, such X-ray CT apparatus having the tube current value and the noise index set independently makes the doctor blindly scans an object to be scanned without knowing whether said system has the scanning condition for the object to be scanned in which the requirements for the tube current value and the noise index are both met.